The present invention relates to an image processing device capable of compensating for a shift of image caused by a shift of original during an image scanning operation.
Conventionally, as an image processing apparatus, an MFP (Multi-Functional Peripheral) having a facsimile function, a copier function, a PC scanning function and a network scanning function has been known. In such an MFP, an original feeder that automatically feeds original sheets is implemented. An image on the original is scanned by adjusting the sheet feed speed with the scanning speed. If a positional relationship between the scanning head and an original table changes slightly due to rattle of the scanning head when the original is fed and vibration occurs, the vibration affects the scanned image.
Japanese Patent Provisional Publication No. P2002-10039 discloses a compensating mechanism, in which a reference mark is formed on the original table to detect a shift of the scanning head with respect to the reference mark, and then, based on the shift as detected, the image data as scanned is compensated.
However, in the above-identified publication, it is assumed that the positional relationship between the original table and the original does not change, and based on the change of the positional relationship between the reference mark on the original table and the scanning head, the image data is compensated. Therefore, in a case where the user place, for example, a book as an original and holds it on the original table by the hand, and the position of the original (book) with respect to the original table is changed due to the vibration of the hands of the user, the scanned image is affected by the displacement of the original even if the compensation method disclosed in the publication is applied.
Incidentally, there is known an image processing device which scans an original on a unit bases. That is, in such a device, units image data consisting of a plurality of lines of image data are successively introduced in an input memory, then compensation processing is applied to the unit image data, which is then stored in a storage. After one unit image data is processed (introduced, compensated and stored), the input memory is released and subsequent unit image data is scanned and introduced. With such a configuration, the performance of the CPU can be relatively low, and the memory size can be saved.
FIG. 11 shows an example of the scanned image 100 which is scanned in accordance with the above-described method, and the original was shifted during scanning as the user's hand was moved. The positions where the shifts occurred in the obtained image are indicated by arrows.
As shown in FIG. 11, the shift of the scanned image appears in a discontinuous manner. If the scanning is performed line by line, the shift in the obtained image appears continuously. However, when the original image is scanned on a block basis, a relatively long time period is required when the input memory is released before the succeeding plurality of lines (i.e., a unit) of image is scanned. If the original is displaced during this relatively long period, the scanned image 100 contains discontinuous sifts in the scanned image as shown in FIG. 11. Such a discontinuous image is conspicuous, which deteriorates the quality of the scanned images.